Carrier frequency shift signaling



Oct. 12, 1948. s. A. BARONE CARRIER FREQUENCY SHIFT SIGNALING Filed April 23, 1946 Space /5 M m i 5 3 mm 2 n MH 0 A 4, 7 j 4 D w Q mm W ZMW A Cm A0 a M BM R A mu 6 7 Fl MR A/Pfi 2 mm MCI r M p :DLR fl )CW ME m m 7 w Mw MT BM ON. r A m TONE KEYER Space Ma f/( /4 1N VEN TOR.

A TTOAIVEY Patented Oct. 12, 1948 UNITED i 2,451,4309; 1 CARRIER FREQUENCY I Salvatore A. Barone, Freeport; .N. -Y.,assignor, 'by

m esne assignments, to Jefierson...Standard.-; Company, a corpo ion of. North.

Broadcasting Carolina Application April 23, 1946, Serial-No. 664 468 7Claims. c1.2.; 'g

This invention relates to Wave signalling systems and more especially to systems of signalling by carrier frequency shift.

A principal object of the invention is to provide an improved method and organization of apparatus for producing frequency-shift carriers whose mean frequency is maintained at an accurately predetermined value.

Another principal object is to provide a carrier frequency-shift radio transmitter wherein a highly stable carrier frequency source such as a crystal-controlled master oscillator, is subjected to a plurality of successive frequency modulation stages in such a way that the mean frequency of the shifted output carrier frequencies is maintained equal to the frequency of said there is produced shifted carrier frequencies having. ahighly stabilized mean frequencyequal to that of said oscillator.

Another feature relates to a carrier frequencymeans to'modulate said main carrier by the frequency-shifted output of one local oscillator, and

means to frequency-shift the modulated main carrier by the frequency-shifted output of the other local oscillator. By means of suitable frequency selector circuits such as band-pass filters or the like, there are selected at the output of the system frequency-shifted carriers whose mean frequency remains equal to the frequency of [said crystal-controlled generator and is substantially independent of accidental changes in the said local oscillator circuits and associated equipment.

A further feature relates to an improved method ofshifting carrier oscillations derived from a crystal-controlled oscillator so that the output carrier has a fixed mean frequency equal to the crystal frequency, the said output mean frequency being shifted equally in opposite direcee .ri 'we e i to t r ta frequ n d corresponding. to telegraph mark and space nals or. the. like.

A.still further featurerelatesto thenovelior ganization, arrangement and relative .interconae nection of. par'tswhich cooperate to proyidegana improved. and flexible carrien frequencyi shifirg telegraph systemand thelike. 1.

Otherfeaturesand advantages not specifically enumerated will be apparent after a considera, tion of the'following detailed the appended claims.

In the drawing which shows one preferred embodiment of the invention, there isrepresented 5 by the numeral In any highlystabilized high frequency oscillator, suchas a temperature-controlled crystal oscillator, which generates the; desired master radio frequency F3 The. output frequency of the system. is indicated Has-,1. (FiZAf), where Af is preferably in the audio.- frequency range, e. g., 400 C. P. S. This output,

can then be considered as two separate carriers,

one having a frequency (F.2A,f) representing; for example a telegraph space signal; and a free, if quency (F+2Af) representing for example a'telegraph mark signal For the purpose of shifting the output frequency between the above-noted limits representing space and mark, there is provided any well-known keying device II, which produces at thepath I 2 a D. C. voltage of for example a positive polarity'and predetermined magnitude when keyed by a space signal and r a D. C. voltage of negative polarity but the same;

magnitude when keyed by a mark signal. ;It

will be understood of course, that the reverse may be true, that is, the space signal maybe repre polarity. and the mark, signal may be represented by the positive polar ity. In any event, and in accordance withlthe 1, present invention, the output of the keyer His 7 sented. by the negative divided into two paths l2, l3, and one pathis designed to produce opposite with respect to that in the cated schematically by the waves, [5.

The signal from path 12 is fed to any suitable,- reactance tube I6, so that the input voltages ape pear in the output of the tube as equivalent xreactance variations. The magnitude of these re.-, actance variations will, in the well-known way, be a function of the amplitude of thetone sig----; nal applied over path l2. ,For a detailed description of a typical reactance tube that may be used,

reference is hereby made to application Serial No. 434,498, filed March 13, 1942; which'issued April 9, 1946, as Patent No. 2,398,054. Likewise,

e. ignal i a h 1 which s ine act phase Sig descriptions and polarity of voltages,., other path as indiexample-only the higher beat' frequencynamel is select'ed for passage byfthe' bangl -pass filter 23;

opposition to the tone signal in path I2, is applied to a similar reactance tube l1.

Associated 'with the output of tube I6 is a local oscillator l8, which may be a free run- 'ning oscillator that need not be controlled to '5 the same degree of accuracy as oscillator Ill, and

which can have its output frequency varied in; accordance'with the reactance variations produced by tube I6. The local oscillator I8 may normally generate a frequency 1, which by way r of example may be thirty k. c, .The oscillatory .control circuit of oscillator ill will include the plate reactance of tube l-B sovthat as the latter is varied by the signals from path 12,:a corre-v sponding change AI is produced in the output frequency of oscillator l8. For a detailed description of one preferred manner of yarying the frequency of oscillator l8, reference may be had to said application Serial No. 434,498. Conse-' quently, there is produced an output frequency from oscillator l8 whichvis (fa-AT) represent.-w ing a telegraph mark signal, and ti jienfl' repre= senting a telegraph space signal; Itlwill beun: derstood of course; that when a mark signal is, beingkeyed at device ll, thejoscillatorxla' may-= generate the frequency (fee-inf), consequently when a space signal vis"being keyed at device H, v oscillator L8 generates'the frequency (f+AJ);..

Ina'similar manner, the reactance'tube il "l con-1 trols thefrequency of waxffree'running 'oscillator 19 which is similar to oscillator: l8, and nor mally generates a frequency 4. Likewise, theoutput of oscillator i9 is variedin frequency'between (f-fiif) and (f+AJ). 'Ho'wever; because ofthe phase opposition of the signals in paths !2 and .I l3,the frequency of oscillatorfil -is changed inth'e j opposite 'direction from-the changein frequencyof oscillator I8: for the same telegraph signal L which is" keyed at device 1H. Inother words-,-if fora space signal at device i L the oscillator l8 produces'a frequenr'zyUfl-Af) ,then simultaneously the oscillatorl9 producesai frequen'cy (fAf)-. Likewise; when oscillator l8 is producingafrequenc'y-lffinfl corresponding to a mark signal' at device ll ,oscillator l9 is producing "a fre-,

The output of oscillator l B-is connected-in balancedfdlvided'relation to any vvell-known bal anc'ed modulator -26, such'for example as'described in Radio Engineering," by Terrnan, "ls t ;edi-" tiong 'pa ge fi5l 'published by McGraw-Hill-Booi; Ce npany,lnc.;, ew Yorkylqijl."Modulator 2e isalso'fed' withthe frequency-l? from'thecry'stal oscillator l9. These two frequencies are mixed in] the 'd evice Zil inthdtvell-knbwh manner so as to produce in the outputthe sum'and difference fre 1' quencies; Inthis type of nod'ulator, the .frequencyF is suppressedinthe output? The double beatfrequenciesfrom the-modulator zeal-sap plied to a band-passfilter 2|,which passes fo i'T F+ f+Af indicatedin the drawing;

The shifted frequency frorn oscillat r {9 like: wise: fed in balanced divided relation to; another balanced modulator-2g, which is alsq fed with th Hf f) s sa item lte Be ause it j balanced modulatoraction of device 22'; the frequency F-l-(fiqf) is suppressedfin' the output. 1 However, "here are present at' this ou put two been, namelYlF-EfifiAj) (1pm 1 s "1 7 I mariner Esra. .7

One vof these lbea'ts ffor example the lower The r-let result is'that the frequeny' at the output ciated equipment.

nal such as a ,mark'vsi nal bynarrier1f menta m x ng w th sa d, frequen y F th a ma from the th of t 4- terminals of filter 23 is (F-l-ZAI) representing a space signal at device II; andlF-ZAI) representing a mark signal at device I I. It will be observed therefore, that the mean frequency F of these two output carrier frequencies always remain equal to, the said frequenc F of the master oscillator 'lfl'; and this mean frequencyremains stable notwithstanding undesired variations' in temperature, humidity and similar iconditions affecting oscillators l3 and i9 and their asso- "By the expression free running as employed inthe claims, is meant'an oscillator which can be '7 set to generate normally a particular frequency a but which frequency can be varied by means of a signal; as distinguished from a fixed frequency oscillator such as a crystal controlled oscillator.

While one particular embodiment has been de- I scribed, it will be understood that various changes and modifications may be made therein Without departing from the spirit and scope of the invei'i tioni i What is' claimed is: i 1. The method of signalling which comprises, generating a master-frequency F,'=genera ting pair of local-auxiliaryfrequencies-each of -fre quencyf, frequency-modulatingboth said l'o'ca frequencies by the same signal: but in opposite respects to produce respective side bands lfi rif) and (fir-A1), mixing the (JJz'A))' frequency 'from one local oscillator with said master" frequency F; and selecting one side band aloneemixing the i! said selected side band. -with the frequency-i (I'IM) from the other-local oscillator," amass- V lecting therefrom '-a side band "com'pone'n L (E:2Af) J, V .2. The method of transmitting a telegraph sig- V nal by carrier frequency shiftwhich? comprises, generating a master'frequencyF which 'repre 1T3 sents the mean between the lirn-its ofthe shifted' carrierfrequencies'to be transmitted, mixing wit saidmaster frequency 'a frequency "1 from a 10" free running carrier source whose frequerio shifted apredetermined amount and. direction i accordance with a telegraph signal such'asa mark signal, selecting one side band of the resulting. mixture, mixing with: said selected sideband l a carrier frequency from another idea]; ifreeii taneously shifted said predeterminedamount-uni. accordance with said signal .butiin the-opposites direction, and selecting fromthe.resulting mir ture a frequency inthe range. (FitZADWmR I T e-inethodiof transmitting ;.a tlcsrap merc shift which compr ses eneratin ree r nn ns-ca riers eac i-thelsame qua- 1 s mult n ousl hif lns he fi e n of both car ier b t in o no te frequency t o s b sa d si na ge erating amaste .-.t d' equ ncy from one of said f res r1 nine rriers a d sel ct ng on s de b u ng with sa s l c ed s de-band rrier; and se e tins efr m the'la' t: mixture the band represented by (Fi' a carrierrequency shifts sna n, a ource emaster frequenc r;

cal u ni e?qsi atorseac e ra in t e sam f eq ency f; graph signals' means responsive to a graph signal suchfasja mark signal f tan'eously shiftingifthe frequencies "of a oscillators substantially thesame amount-tut opposite frequency directions, means to mix the output of one oscillator with said master frequency F and to select one side band from the resultant mixture, means to mix said selected side band with the shifted frequency from the other local oscillator, and means to select from the last-mentioned mixture a frequency in the range (FiZAf), where Af represents the extent of frequency shift in said local oscillators.

5. In a carrier frequency shift signalling system, a source of master carrier frequency F, a telegraph tone keyer, a pair of shiftable frequency local oscillators each normally generating the same frequency f, means to apply keyed tone signals simultaneously to both said oscillators to shift their respective output frequencies substantially equal amounts but in opposite directions, a first balanced modulator which is fed with said master frequency F and with the shifted frequency from one local oscillator, means to select from the output of said first balanced modulator a sideband frequency F+(I:Af), another balanced modulator which is fed with a selected side band from the first balanced modulator and with the shifted frequency from the second local oscillator, and means to select from the output of said second balanced modulator a band represented by (FiZAf) where A represents the extent of frequency shift in said local oscillators.

6. In a carrier frequency shift signalling systerm, a source of master frequency F, a source of keyed telegraph signals, a pair of balanced modulators, a plurality of separate paths leading from said keyer respectively to said balanced modulators, each of said paths including in series a local shiftable frequency oscillator and a reactance tube, each oscillator generating normally the same frequency 1, means to vary the plate reactances of the .tubes in said paths to produce opposite frequency shifts in said local oscillators under control of said keyed signals, a selector system in the form of a band-pass filter for selecting from t pu 0 t e fir t bala ced medulator a sideband F-l-(fiAf) and a selector system in the form of a band-pass filter connected to the output of the second balanced modulator for selecting a frequency in the range (FiZAf) where M represents the extent of frequency shift in said local oscillators under control of said keyed signals.

7. In a carrier frequency shift signalling systerm, a source of master frequency F, a local shiftable frequency oscillator of normal frequency f,

. a first mixing network upon which the said master frequency F and said local oscillations are impressed said mixing network acting to suppress said frequency F, means to shift the frequency of said local oscillator over the range (fi-Af) under control of one telegraph signal, means to select from the output of said first network a frequency band F-i-(fi-Af), a second local shiftable frequency oscillator of normal frequency f, a second mixing network upon which the said frequencies F-i-(fiAf) are impressed together with the oscillations from said second oscillator, said second network acting to suppress the range of frequencies F+ (fztAf), and means to select from the output of said second network a frequency in the band (FiZAf).

SALVATORE A. BARONE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

